A very fast control based on hysteresis of the Cout current with a frequency loop to operate at constant frequency

Abstract

The combination of non-linear control and linear control proposed in [1] provides very fast transient response (voltage step from 1 V to 1.5 V in 2 ¿s). This non-linear control is based on hysteretic control of the Cout current. This system is very sensitive to effects like aging, temperature, input and output voltage variation, etc., that modify the switching frequency. This paper proposes a frequency loop to avoid the frequency variation and to adjust the switching frequency to the nominal value by changing the hysteretic band. The design and analysis of the nonlinear loop, the voltage loop and frequency loop are presented in detail with a design example. A 5 MHz buck converter is developed and experimental results validate the loops design, obtaining the same fast transient response (from 1.5 V to 2.5 V in 2 ¿s) but keeping constant the switching frequency in steady state.